U.S. patent application number 10/227793 was filed with the patent office on 2003-03-20 for photovoltaically active materials and cells containing them.
Invention is credited to Kuhling, Klaus, Sterzel, Hans-Josef.
Application Number | 20030051752 10/227793 |
Document ID | / |
Family ID | 26010037 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030051752 |
Kind Code |
A1 |
Sterzel, Hans-Josef ; et
al. |
March 20, 2003 |
Photovoltaically active materials and cells containing them
Abstract
In a photovoltaic cell having a photovoltaically active
semiconductor material constituted by a plurality of metals or
metal oxides, the photovoltaically active material is selected from
a p- or n-doped semiconductor material constituted by a ternary
compound of the general formula (I)
Me.sub.xS.sup.A.sub.yS.sup.B.sub.z (I) with Me=Al, Ti, Zr, V, Nb,
Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu or Ag, S.sup.A, S.sup.B=B, C, Si,
Ge, Sb, Se or Te, where S.sup.A and S.sup.B respectively come from
different groups of the periodic table, x, y, z are independent of
one another and can take values from 0.01 to 1, and where the
proportion by weight of S.sup.A and S.sup.B together is no more
than 30%, expressed in terms of the total semiconductor material,
or a mixed oxide of the general formula (II) 1 [ ( CaO ) u ( SrO )
v ( BaO ) w ( 1 / 2 Bi 2 O 3 ) x ] f 2 n + a 2 ( { k } Me n O n 2 {
2 - k } Me n + a O n + a 2 ) ( II ) with Me=Fe, Cu, V, Mn, Sn, Ti,
Mo, W n=integer from 1 to 6, a=1 or 2, f=number from 0.2 to 5,
k=number from 0.01 to 2, u+v+w+x=1.
Inventors: |
Sterzel, Hans-Josef;
(Dannstadt-Schauernheim, DE) ; Kuhling, Klaus;
(Mutterstadt, DE) |
Correspondence
Address: |
Herbert B. Keil
KEIL & WEINKAUF
1350 Connecticut Ave., N.W.
Washington
DC
20036
US
|
Family ID: |
26010037 |
Appl. No.: |
10/227793 |
Filed: |
August 27, 2002 |
Current U.S.
Class: |
136/252 ;
136/261; 136/264; 136/265; 257/E31.026; 438/93; 438/95 |
Current CPC
Class: |
H01L 31/032
20130101 |
Class at
Publication: |
136/252 ;
136/265; 136/264; 136/261; 438/93; 438/95 |
International
Class: |
H01L 031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2001 |
DE |
10142632.1 |
May 28, 2002 |
DE |
102 23 744. 1 |
Claims
We claim:
1. A photovoltaic cell having a photovoltaically active
semiconductor material constituted by a plurality of metals or
metal oxides, wherein the photovoltaically active material is
selected from a p- or n-doped semiconductor material constituted by
a ternary compound of the general formula (I)
Me.sub.xS.sup.A.sub.yS.sup.B.sub.z (I) with Me=Al, Ti, Zr, V, Nb,
Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu or Ag, S.sup.A, S.sup.B=B, C, Si,
Ge, Sb, Se or Te, where S.sup.A and S.sup.B respectively come from
different groups of the periodic table, x, y, x are independent of
one another and can take values from 0.01 to 1, and where the
proportion by weight of S.sup.A and S.sup.B together is no more
than 30%, expressed in terms of the total semiconductor material,
or a mixed oxide of the general formula (II) 4 [ ( CaO ) u ( SrO )
v ( BaO ) w ( 1 / 2 Bi 2 O 3 ) x ] f 2 n + a 2 ( { k } Me n O n 2 {
2 - k } Me n + a O n + a 2 ) ( II ) with Me=Fe, Cu, V, Mn, Sn, Ti,
Mo, W n=integer from 1 to 6, a=1 or 2, f=number from 0.2 to 5,
k=number from 0.01 to 2, u+v+w+x=1.
2. A photovoltaic cell as claimed in claim 1, wherein, in the
semiconductor material, S.sup.A and S.sup.B are selected from B, C,
Ge, Sb and Te.
3. A photovoltaic cell as claimed in claim 1, wherein, in the
semiconductor material, Me is selected from Al, Ti and Zr.
4. A photovoltaic cell as claimed in claim 1, wherein, in the
semiconductor material, Me is selected from V, Nb and Ta.
5. A photovoltaic cell as claimed in claim 1, wherein, in the
semiconductor material, Me is selected from Cr, Mo or W.
6. A photovoltaic cell as claimed in claim 1, wherein, in the
semiconductor material, Me is selected from Mn, Fe, Co and Ni.
7. A photovoltaic cell as claimed in claim 1, wherein, in the
semiconductor material, Me is selected from Cu and Ag.
8. A photovoltaic cell as claimed in claim 1, wherein, for the
mixed oxide, f has a value in the range from 0.2 to 0.9 or 1 or
from 1.01 to 2 or from 2.01 to 5.
9. A photovoltaically active material as defined in claim 1, except
for ternary compounds constituted by AlB.sub.12 and SiB.sub.6.
10. A process for the preparation of semiconductor materials as
claimed in claim 9, by sintering or melting together and
subsequently sintering mixtures of the element powders or by
sintering mixtures of the oxide powders, extruding to form strips
and optionally stretching the strips during the subsequent cooling
below the material melting point.
11. A process for the combinatorial preparation and testing of
semiconductor materials for photovoltaic cells as claimed in claim
9, in which an array of thin-film dots of the semiconductor
materials with different composition is produced on a conductive
two-dimensional substrate, the substrate is heat-treated with the
array to a desired measurement temperature and the dots are
respectively brought into contact with a measurement pin, the
voltage without load, the current and the voltage with a decreasing
load resistance and/or the short-circuit current being measured
under illumination, subsequently stored and evaluated.
12. An array of at least 10 different semiconductor materials as
claimed in claim 9 on a conductive substrate.
13. A process for the preparation of photovoltaic cells as claimed
in claim 1, by applying layers of the semiconductor material to
conductive substrates by means of screen printing.
Description
[0001] The invention relates to photovoltaically active materials
and to photovoltaic cells containing them.
[0002] Photovoltaic cells have been used for a long time to obtain
electrical energy from sunlight. To date, in particular,
crystalline silicon solar cells have been used in this context, the
efficiency of which it has been possible to improve by more than
50% in the last 15 years. However, the solar cells available to
date still have a property spectrum which could be improved.
[0003] The currently best commercially available photovoltaic cells
have efficiencies of only 17-18%. Purely theoretically,
efficiencies of up to 33% are achievable with silicon-based cells.
A description of the state of the art in the development of solar
cells can be found in M. A. Green et al., Solar Energy Materials
& Solar Cells 65 (2001), pages 9-16 and M. A. Green, Materials
Science and Engineering B74 (2000), pages 118-124.
[0004] The maximum efficiency during the conversion of sunlight
into electrical energy is, for thermodynamic reasons, about 93%.
Owing to a number of mechanisms, electron-hole pairs that have been
separated by photons become recombined, which reduces the
efficiency greatly.
[0005] The electrons, which are raised by the incident photons from
the valence band of the semiconductor into the conduction band,
initially still have the extra energy which corresponds to the
energy of the photon less the band gap. The energy surplus is
gradually lost nonradiatively by collisions with lattice
vibrations, which heats the material. Finally, the charge carriers
recombine in a statistical fashion with a further loss of
efficiency. Taking all the loss mechanisms into account, maximum
efficiencies of about 33% can be achieved with silicon as the
photovoltaic material.
[0006] An essential task in materials research currently consists
in finding photovoltaically active materials which exhibit these
loss mechanisms to a much lesser extent.
[0007] Solutions to this involve materials having a multiplicity of
subbands in the valence band structure, which are excited by
photons of high to low wavelengths, so as thereby to promote
electrons respectively into the conduction band. A multiplicity of
subbands is obtained in materials having a complex crystal
structure which form, for example, sublattices.
[0008] It is also necessary for collisions between electrons and
lattice vibrations, i.e. collisions between electrons and phonons,
to be avoided as far as possible, in order to avoid the
recombination of electrons and holes. The motion of electrons and
phonons needs to be decoupled as far as possible.
[0009] There is still a need for photovoltaically active materials
which have a high efficiency and exhibit a suitable property
profile for different application fields. Research in the field of
photovoltaically active materials can by no means yet be regarded
as concluded, so that there is still a demand for different
photovoltaic materials.
[0010] It is an object of the present invention to provide
photovoltaically active materials and photovoltaic cells containing
them, which avoid the disadvantages of existing materials and cells
and, in particular, have higher efficiencies.
[0011] We have found that this object is achieved by a photovoltaic
cell having a photovoltaically active semiconductor material
constituted by a plurality of metals or metal oxides, wherein the
photovoltaically active material is selected from a p- or n-doped
semiconductor material constituted by a ternary compound of the
general formula (I)
Me.sub.xS.sup.A.sub.yS.sup.B.sub.z (I)
[0012] with
[0013] Me=Al, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu or
Ag,
[0014] S.sup.A, S.sup.B=B, C, Si, Ge, Sb, Se or Te,
[0015] where S.sup.A and S.sup.B respectively come from different
groups of the periodic table,
[0016] x, y, z are independent of one another and can take values
from 0.01 to 1,
[0017] and where the proportion by weight of S.sup.A and S.sup.B
together is no more than 30%, expressed in terms of the total
semiconductor material,
[0018] or a mixed oxide of the general formula (II) 2 [ ( CaO ) u (
SrO ) v ( BaO ) w ( 1 / 2 Bi 2 O 3 ) x ] f 2 n + a 2 ( { k } Me n O
n 2 { 2 - k } Me n + a O n + a 2 ) ( II )
[0019] with
[0020] Me=Fe, Cu, V, Mn, Sn, Ti, Mo, W
[0021] n=integer from 1 to 6,
[0022] a=1 or 2,
[0023] f=number from 0.2 to 5,
[0024] k=number from 0.01 to 2, preferably from 0.01 to 1.99, e.g.
1
u+v+w+x=1.
[0025] The photovoltaic cells according to the invention enhance
quite generally, on the one hand, the range of available
photovoltaic cells. Owing to the different chemical systems, it is
possible to satisfy different requirements in various application
fields of the photovoltaic cells. The photovoltaic cells according
to the invention hence significantly extend the possibilities for
application of these elements under different conditions.
[0026] The photovoltaic cells contain, besides the photovoltaically
active material, preferably optically transparent, electrically
conductive cover layers such as indium tin oxide and electrically
conductive substrate materials, between which the photovoltaically
active material is situated.
[0027] The invention relates to semiconductor materials, except for
ternary compounds constituted by AlB.sub.12 and SiB.sub.6.
[0028] Preferred semiconductor materials will be explained in more
detail below.
[0029] In the ternary compounds of the general formula (I), S.sup.A
and S.sup.B are preferably selected from B, C, Ge, Sb and Te.
[0030] In this semiconductor material, Me is preferably selected
from one of the following groups:
[0031] 1) Al, Ti, Zr.
[0032] 2) V, Nb, Ta
[0033] 3) Cr, Mo, W
[0034] 4) Mn, Fe, Co, Ni
[0035] 5) Cu, Ag.
[0036] The proportion of doping elements is up to 0.1 atom % in the
alloy, or from 10.sup.18 to 10.sup.20 charge carriers per cubic
centimeter. Higher charge-carrier concentrations cause
disadvantageous recombinations, and hence a reduced charge
mobility. The doping is carried out with elements which cause an
electron surplus or deficit in the crystal lattice, e.g. with
iodide for n-type semiconductors and alkaline earth elements for
p-type semiconductors, so long as a 3/5 or {fraction (3/6)}
semiconductor is present.
[0037] A further possible way of doping is obtained if holes or
electrons are deliberately introduced into the materials by means
of super- or substoichiometric compositions, which obviates the
need for an additional doping step.
[0038] Dopant elements may also, however, be introduced via aqueous
solutions of metal salts, which are subsequently dried in the
mixture. The metal cations are then reduced e.g. by hydrogen at
elevated temperatures or remain in the material without reduction.
Preferably, the p- or n-doping is carried out through selection of
the quantitative proportions of the compounds, or the p-doping is
carried out with alkali metals and the n-doping with Sb, Bi, Se, C,
Te, Br or I (see WO 92/13811).
[0039] The materials according to the invention of the general
formula (I) are prepared by known methods, the element compounds
e.g. by sintering the element powders at high temperatures, but
below the melting point, or by melting in a high vacuum and
subsequently powdering and sintering or by melting the mixture of
element powders and cooling.
[0040] In the mixed oxides of the general formula (II), n denotes
the oxidation state of the metal Me and f denotes a stoichiometric
factor. f has a value in the range from 0.2 to 5, preferably 0.5 to
2, particularly preferably 1. a indicates the difference between
the two different oxidation states of Me.
[0041] For the stoichiometric factor f, numbers from 0.2 to 0.99,
the value 1, numbers from 1.01 to 2 and numbers from 2.01 to 5 may
be indicated as preferred ranges.
[0042] Each of these cases involves a preferred embodiment of the
invention.
[0043] k denotes the respective amounts of the oxidation
states.
[0044] The expression in brackets 3 ( { k } Me n O n 2 { 2 - k } Me
n + a O n + a 2 )
[0045] may preferably be, specifically:
[0046] FeO//Fe.sub.2O.sub.3
[0047] Cu.sub.2O//CuO
[0048] VO//V.sub.2O.sub.3
[0049] V.sub.2O.sub.3//V.sub.2O.sub.5
[0050] VO.sub.2//V.sub.2O.sub.5
[0051] VO.sub.2//V.sub.2O.sub.3
[0052] MnO//Mn.sub.2O.sub.3
[0053] Mn.sub.2O.sub.3//Mn.sub.2O.sub.3
[0054] SnO//SnO.sub.2
[0055] TiO//Ti.sub.2O.sub.3
[0056] Ti.sub.2O.sub.3 //TiO.sub.2
[0057] MoO.sub.2//MoO.sub.3 or
[0058] WO.sub.2//WO.sub.3, especially preferably
[0059] FeO.1/2Fe.sub.2O.sub.3
[0060] 1/2Cu.sub.2O.CuO
[0061] VO.1/2V.sub.2O.sub.3
[0062] V.sub.2O.sub.3.V.sub.2O.sub.5
[0063] VO.sub.2.1/2V.sub.2O.sub.5
[0064] VO.sub.2.1/2V.sub.2O.sub.3
[0065] MnO.1/2Mn.sub.2O.sub.3
[0066] 1/2Mn.sub.2O.sub.3.1/2Mn.sub.2O.sub.3
[0067] SnO.SnO.sub.2
[0068] TiO.1/2Ti.sub.2O.sub.3
[0069] 1/2Ti.sub.2O.sub.3.TiO.sub.2
[0070] MoO.sub.2.MoO.sub.3or
[0071] WO.sub.2.WO.sub.3
[0072] The mixed oxides according to the invention are prepared
using known methods, preferably by intimate mixing of the
individual oxides by known ceramic technologies, pressing the
mixtures under pressure to form moldings of, for example, cuboid
configuration, and sintering the moldings in an inert atmosphere,
e.g. under argon, at temperatures from 900 to 1700.degree. C.
[0073] The materials according to the invention are hence prepared
by known methods, the element compounds e.g. by sintering the
element powders at high temperatures, but below the melting point,
or by melting in a high vacuum and subsequently powdering and
sintering. The oxides are synthesized e.g. by sintering the powder
mixtures of the individual oxides. The expression combinatorial, as
used above, refers specifically to this preparation, in particular
the sintering.
[0074] The photovoltaically active mixed oxides can also be
prepared by reactive sintering of the corresponding metal mixtures
in air at elevated temperatures. For economic reasons, it is also
expedient to use mixtures of oxides and metals.
[0075] It is also an object of the invention to optimize the
materials in terms of efficiency. It is obvious that, when the
components are varied by, for example, 5 atom %, very many
materials need to be synthesized and tested. We have found that
this object is achieved by combinatorial methods. To that end,
element alloys or oxide mixtures or mixtures of elements with
oxides, with gradual variation of the composition as a function of
the length coordination on a substrate, can be produced by
producing the elements or already binary alloys, from appropriate
targets, on a substrate provided with a perforated mask, the
element composition changing as a function of the distance from the
target or as a function of the sputtering angle. The mask is
subsequently removed, and the thin-film "dots" which are produced
are sintered to form the actual materials. The expression "dot"
refers in this case to points or regions of the material which are
spatially separated from one another on a substrate, which have
essentially the same extents and which are preferably arranged at
regular intervals, so that an array is obtained. "Array" means a
two-dimensional, essentially uniformly spaced arrangement of dots
on a substrate surface. It is also possible to suspend element and
oxide powders having particle sizes smaller than 5 .mu.m in an
inert suspension medium, such as hydrocarbons, with the
participation of a dispersing agent to form sufficiently stable
suspensions, and to deposit mixtures of the suspensions as
droplets, in the manner described for the oxides, to evaporate the
suspension medium and to sinter on the substrate the powder
mixtures formed in this way.
[0076] Besides metallic substrates, silicon carbide, which is also
sufficiently electrically conductive, is preferred as an inert
substrate material which is stable with respect to temperature and
diffusion.
[0077] Thin-film dots of the oxides can be produced on a substrate
surface by using doping machines to deposit mixtures of salts,
preferably nitrates or other soluble compounds, in the form of
drops with variable composition, evaporating the solvent,
preferably water, converting the nitrates or compounds into the
oxides by raising the temperature and subsequently sintering the
oxide mixtures in their entirety.
[0078] Per substrate plate with dimensions of the order of 10*10
cm, from 1000 to 10,000 dots with size (diameters) of from 0.2 to 2
mm are applied.
[0079] Fast and reliable testing of the materials is essential.
According to the invention, the following analysis method may be
implemented for this purpose:
[0080] The invention relates to a process for the combinatorial
preparation and testing of semiconductor materials for photovoltaic
cells, in which an array of thin-film dots of the semiconductor
materials with different composition is produced on a conductive
two-dimensional substrate, the substrate is heat-treated,
preferably under an inert gas such as nitrogen or argon, with the
array to a desired measurement temperature and the dots are
respectively brought into contact with a measurement pin, the
voltage without load, the current and the voltage with a decreasing
load resistance and/or the short-circuit current being measured
under illumination, subsequently stored and evaluated. The
illumination may be varied in this case.
[0081] For the method, the dots situated on the metallic or
silicon-carbide substrate are ground to a uniform height e.g. by
using a microfine grinding disk, a plane surface with a small
roughness depth being obtained at the same time. The substrate
plate is brought to a measurement temperature, and the dots are
brought into contact with a measurement pin under a defined
application force.
[0082] While the measurement pin is being applied, the voltage
without load, the current and the voltage with a decreasing load
resistance as well as the short-circuit current are measured.
Computer controlled measurement equipment requires about 10 seconds
in order to measure one material, including travel to the next dot,
which makes it possible to measure approximately 10,000 dots per
day at one temperature. If the operation is carried out with a
plurality of measurement pins in parallel, then a correspondingly
larger number of dots can be measured. The measured values and
curves can be stored and graphically processed, so that a graphical
representation indicates, at a glance, the better materials whose
composition is then analyzed using standard methods. Operation is
preferably carried out under an inert gas.
[0083] The also invention relates to an array of at least 10
different semiconductor materials according to the invention on a
conductive substrate.
[0084] The materials according to the invention are introduced into
modules, as described e.g. in WO 98/44562, U.S. Pat. No. 5,448,109,
EP-A-1 102 334 or U.S. Pat. No. 5,439,528, and these modules are
connected in series.
* * * * *